Thibor v15x crashes, Thibor v14 doesn't

The router is Linksys WRT54G v2.2. Thibor v15 crashes consistently and reproducibly when I try to copy a large file (650 MB) from a wireless client to a wired client. I did do "Clear NVRAM, restore factory defaults", so this is not the issue. Upgraded to v15b1, the problem remains. Tried both WPA and WPA2.

When I downgraded to v14, the problem disappeared completely and the router is rock-solid again.